Which service allows users to publish and monitor APIs?

The correct answer is the service that specifically enables users to publish, maintain, monitor, and secure APIs at any scale. Amazon API Gateway is designed to facilitate the creation and management of APIs, allowing developers to define endpoints, handle requests, and seamlessly integrate with backend services such as AWS Lambda or any other AWS service. This service efficiently handles tasks such as traffic management, authorization and access control, and version management, all of which are essential for robust API management.

Additionally, Amazon API Gateway provides built-in monitoring features that allow users to track API usage and performance metrics through Amazon CloudWatch, making it a powerful tool for both developers and businesses looking to deploy APIs effectively. This includes setting up custom domain names for APIs and generating API keys for managing access, which further strengthens its role as a comprehensive API management solution.

The other services listed do not focus primarily on API management. Instead, they serve different purposes within the AWS ecosystem.